1. Field of the Invention
The present invention relates to a differential gear which is applicable to a transaxle apparatus equipped on a vehicle such as a riding lawn tractor.
2. Related Art
Conventionally, there is a well-known differential gear for differentially connecting left and right axles with each other, comprising a pair of side bevel gears fixed on the respective axles, at least one bevel pinion engaging with both side bevel gears, and a differential gear casing which rotatably supports the bevel pinion.
The differential gear designed as mentioned above is provided on a vehicle so that its differential gear casing is rotated by driving power of an engine for driving the axles. The differential gear, during the turning of the vehicle, automatically adjusts the difference of rotary speed between an inside drive wheel and an outside drive wheel, thereby ensuring a smooth turning of the vehicle and preventing the drive wheels from abrasion.
However, this type of differential gear has the problem that when one of the drive wheels runs idle over a muddy or snow-covered place, the driving power is not transmitted to the other drive wheel.
In consideration of the problem, it is proposed and well-known as disclosed in U.S. Pat. No. 5,897,452, for example, that the conventional differential gear is further provided therein with a kind of brake which applies a braking force onto one of the drive wheels being about to run idle so as to give driving power to the other drive wheel. This is what is called a limited-slip differential.
For traveling on a bad road which is muddy, snow-covered or such, it is also well-known that the conventional differential gear is further alternatively with a differential locking system for locking both the axles together. This differential gear system is applicable to an agricultural vehicle which is desired to travel properly straight on a field.
However, lightening, cost-saving and compacting of the conventional differential gear system, including the limited-slip differential or the differential locking system, is disturbed by the structure thereof such that the bevel pinion is supported by the differential gear casing through pinion shafts.
An object of the present invention is to provide a limited-slip differential gear with a differential locking mechanism, preferably being minimized and reducing cost.
To achieve the object, according to the present invention, a pair of side bevel gears are fixed onto respective axles. A bevel pinion engages with both the side bevel gears. Preferably an input gear is provided with a through hole in which the bevel pinion is disposed so that a differential gear casing becomes unnecessary, thereby enabling a light, compact and cost-saving differential gear to be provided.
A lock member selectively bringing one of the side bevel gears into non-relatively rotatable connection with the input gear is provided for convenience in steadily travelling on unstable ground such as mud, snowcovered or the like. A certain friction force is applied onto the side bevel gears through the bevel pinion, thereby constituting a limitedslip differential gear. The resulting limited-slip differential gear provided with a locking system is light, compact and cost-saving.
Preferably, a pinion shaft is provided for rotatably supporting the bevel pinion therearound while the pinion shaft applies a certain brake force onto the bevel pinion. In this case, the pinion shaft is disposed in the through hole of the input gear.
The present limited-slip differential gear provided with a locking system may be disposed in a transaxle apparatus. Preferably, the transaxle apparatus is constructed so that the present differential gear and a hydrostatic transmission are disposed in a common housing, wherein the input gear of the differential gear receives the output of the hydrostatic transmission. Consequently, the transaxle apparatus is light, compact and cost-saving.
Other and further objects, features and advantages of the invention will appear more fully from the following description.